1. Field of the Invention
The present invention relates generally to the field of telecommunications. More particularly, the present invention relates to methods and apparatus for the set-up and implementation of multimedia multipoint communications utilizing the ATM network. The invention has particular application to distance learning, although it is not limited thereto.
2. State of the Art
Perhaps the most awaited, and now fastest growing technology in the telecommunication field in the 1990's is known as Asynchronous Transfer Mode (ATM) technology. ATM is providing a mechanism for removing performance limitations of local area networks (LANs) and wide area networks (WANs) and providing data transfers at speeds of on the order of gigabits and even terabits/second. The variable length packets of LAN and WAN data are being replaced with ATM cells which are relatively short, fixed length packets. Because ATM cells can carry voice, video and data across a single backbone network, the ATM technology provides a unitary mechanism for high speed end-to-end telecommunications traffic. In addition, each ATM connection is provided with a guaranteed level of service.
With the ability to transfer voice, video and data across a single backbone network, ATM technology has become a natural selection for implementing multimedia (e.g., audio and video) telecommunications. While still in its infancy, multimedia telecommunications, including video-conferencing, is expected to be an area of extremely large growth in the coming years. One area of multimedia telecommunications which is of importance is multimedia, multipoint telecommunications; e.g., video-conferencing with multiple parties. Multimedia, multipoint telecommunications has several applications, including group conferencing at multiple sites, and distance learning.
The field of distance learning typically involves a teacher located at a first location (main classroom), and students located at several different remote locations (remote classrooms). Preferably, in distance learning applications, communications are multi-directional; i.e., the teacher can be seen and heard by the students in the remote locations, and the students at the remote locations can be controllably seen and heard by the teacher and by each other. Control of who is seen and heard is preferably provided to the teacher in the main classroom.
Several different mechanisms for implementing distance learning have been utilized or proposed in the art. As seen in prior art FIG. 1, according to a first prior art arrangement, a call is set up using a cross-connect switch 10 in a standard telecommunications network 15 (i.e., non-ATM-network) between the main classroom 20a, and the remote classrooms 20b-20d, and between each remote classroom and the other remote classrooms and the main classroom. In order to provide multimedia multipoint communications using the standard telecommunications network, large bandwidth dedicated-subscriber lines (e.g., T3) and complex equipment are required for each of the classroom sites. Of course, the cost of maintaining such large bandwidth lines is extremely high, as the line is dedicated (i.e., not switched) and provides an around-the-clock connection, regardless of whether that connection is to be used frequently or infrequently. The cross-connect switch 10 under application software control provides the necessary switching function to emulate the multidirectional connectivity.
Turning to FIG. 2, a first proposed ATM solution to multimedia multipoint communications is shown. In FIG. 2 the ATM network 25 is utilized by the main classroom 40a and the remote classrooms 40b-40d. According to the proposal, two choices in establishing multiple circuits directly between the classrooms are available. A first arrangement involves, at a desired time, using a network manager 30 to provide permanent virtual circuits (PVCs) between each classroom and the ATM network 25 in order to guarantee the availability of the connections. The problem with utilizing PVCs however, is that a meshed network of PVCs connecting each site to the others would be required. The cost of such an arrangement is high, as every location which wishes to be a party to the distance learning application must pay for PVCs to all other locations. In addition, expensive equipment which terminates the mesh of PVCs would be required at every site. To avoid the costs associated with the use of PVCs, and in accord with a second arrangement, the multiple circuits can be established on an as-need basis using switched virtual circuits (SVCs). The problem with utilizing SVCs however, is that each time a connection is needed, (e.g., to add another remote classroom, or to permit a remote classroom to talk) a new circuit must be established which entails a call setup procedure which can take several seconds, particularly where a multipoint connections is required. Indeed, the delay can get even longer when the network is busy, and it is possible the connection can be refused. This interruption of at a minimum several seconds effectively destroys the flow of conversation, and is undesirable in both classroom and multipoint group conferencing situations.
In order to overcome some of the problems of the prior art proposals, there have been additional proposals as seen in FIGS. 3a and 3b to use a multimedia multipoint server 60 in order to establish multimedia multipoint connections between a main classroom 70a and a plurality of remote classrooms 70b-70d via the ATM network 75. In the arrangements of FIGS. 3a and 3b, PVCs or SVCs are established between the classrooms and the multimedia multipoint server 60. In particular, at a designated time, which typically requires prior reservation of the resources of the multipoint server, connections are placed to the server 60 which is programmed to accept the connections and set up the conference. In the arrangement of FIG. 3a, it is seen that the multimedia multipoint server receives audio and video information from each of the classrooms, mixes the information as desired, and forwards copies of the mixed information to the different classrooms. it is noted that the main classroom may receive a mix of information from the remote classrooms, while each of the remote classrooms may receive a copy of information from the main classroom, or from the remote classroom which is asking a question. In the arrangement of FIG. 3b, a similar arrangement is seen, except that instead of sending out multiple copies of information from the multimedia multipoint server, a single copy is sent into the ATM network, and duplicated as required at various switches in the ATM network. Thus, only the classroom with an active speaker or with the student asking a question is seen at each of the other classrooms.
Regardless of whether the arrangement of FIG. 3a or FIG. 3b is utilized, it will be appreciated that the costs associated with establishing the multimedia multipoint conference are high. In particular, the tariff for the use of multimedia multipoint server resources is very high, even where a single output port (FIG. 3b) is being utilized.